﻿// Copyright (c) 2024 Quetzal Rivera.
// Licensed under the MIT License, See LICENCE in the project root for license information.

using System.ComponentModel;
using System.Diagnostics;
using System.Runtime.InteropServices;

namespace Vite.AspNetCore.Services;

/// <summary>
/// Allows processes to be automatically killed if this parent process unexpectedly quits.
/// This feature requires Windows 8 or greater. On Windows 7, nothing is done.</summary>
/// <remarks>
/// From:
/// https://stackoverflow.com/questions/3342941/kill-child-process-when-parent-process-is-killed
/// References:
///  https://stackoverflow.com/a/4657392/386091
///  https://stackoverflow.com/a/9164742/386091 </remarks>
static class ChildProcessTracker
{
    /// <summary>
    /// Add the process to be tracked. If our current process is killed, the child processes
    /// that we are tracking will be automatically killed, too. If the child process terminates
    /// first, that's fine, too.</summary>
    /// <param name="process"></param>
    public static void AddProcess(Process process)
    {
        if (s_jobHandle != IntPtr.Zero)
        {
            bool success = AssignProcessToJobObject(s_jobHandle, process.Handle);
            if (!success && !process.HasExited)
                throw new Win32Exception();
        }
    }

    static ChildProcessTracker()
    {
        // This feature requires Windows 8 or later. To support Windows 7 requires
        //  registry settings to be added if you are using Visual Studio plus an
        //  app.manifest change.
        //  https://stackoverflow.com/a/4232259/386091
        //  https://stackoverflow.com/a/9507862/386091
        if (Environment.OSVersion.Version < new Version(6, 2))
            return;

        // The job name is optional (and can be null) but it helps with diagnostics.
        //  If it's not null, it has to be unique. Use SysInternals' Handle command-line
        //  utility: handle -a ChildProcessTracker
        string jobName = "ChildProcessTracker" + Process.GetCurrentProcess().Id;
        s_jobHandle = CreateJobObject(IntPtr.Zero, jobName);

        var info = new JOBOBJECT_BASIC_LIMIT_INFORMATION();

        // This is the key flag. When our process is killed, Windows will automatically
        //  close the job handle, and when that happens, we want the child processes to
        //  be killed, too.
        info.LimitFlags = JOBOBJECTLIMIT.JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE;

        var extendedInfo = new JOBOBJECT_EXTENDED_LIMIT_INFORMATION();
        extendedInfo.BasicLimitInformation = info;

        int length = Marshal.SizeOf(typeof(JOBOBJECT_EXTENDED_LIMIT_INFORMATION));
        IntPtr extendedInfoPtr = Marshal.AllocHGlobal(length);
        try
        {
            Marshal.StructureToPtr(extendedInfo, extendedInfoPtr, false);

            if (
                !SetInformationJobObject(
                    s_jobHandle,
                    JobObjectInfoType.ExtendedLimitInformation,
                    extendedInfoPtr,
                    (uint)length
                )
            )
            {
                throw new Win32Exception();
            }
        }
        finally
        {
            Marshal.FreeHGlobal(extendedInfoPtr);
        }
    }

    [DllImport("kernel32.dll", CharSet = CharSet.Unicode)]
    static extern IntPtr CreateJobObject(IntPtr lpJobAttributes, string name);

    [DllImport("kernel32.dll")]
    static extern bool SetInformationJobObject(
        IntPtr job,
        JobObjectInfoType infoType,
        IntPtr lpJobObjectInfo,
        uint cbJobObjectInfoLength
    );

    [DllImport("kernel32.dll", SetLastError = true)]
    static extern bool AssignProcessToJobObject(IntPtr job, IntPtr process);

    // Windows will automatically close any open job handles when our process terminates.
    //  This can be verified by using SysInternals' Handle utility. When the job handle
    //  is closed, the child processes will be killed.
    private static readonly IntPtr s_jobHandle;
}

enum JobObjectInfoType
{
    AssociateCompletionPortInformation = 7,
    BasicLimitInformation = 2,
    BasicUIRestrictions = 4,
    EndOfJobTimeInformation = 6,
    ExtendedLimitInformation = 9,
    SecurityLimitInformation = 5,
    GroupInformation = 11
}

[StructLayout(LayoutKind.Sequential)]
struct JOBOBJECT_BASIC_LIMIT_INFORMATION
{
    public Int64 PerProcessUserTimeLimit;
    public Int64 PerJobUserTimeLimit;
    public JOBOBJECTLIMIT LimitFlags;
    public UIntPtr MinimumWorkingSetSize;
    public UIntPtr MaximumWorkingSetSize;
    public UInt32 ActiveProcessLimit;
    public Int64 Affinity;
    public UInt32 PriorityClass;
    public UInt32 SchedulingClass;
}

[Flags]
enum JOBOBJECTLIMIT : uint
{
    JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE = 0x2000
}

[StructLayout(LayoutKind.Sequential)]
struct IO_COUNTERS
{
    public UInt64 ReadOperationCount;
    public UInt64 WriteOperationCount;
    public UInt64 OtherOperationCount;
    public UInt64 ReadTransferCount;
    public UInt64 WriteTransferCount;
    public UInt64 OtherTransferCount;
}

[StructLayout(LayoutKind.Sequential)]
struct JOBOBJECT_EXTENDED_LIMIT_INFORMATION
{
    public JOBOBJECT_BASIC_LIMIT_INFORMATION BasicLimitInformation;
    public IO_COUNTERS IoInfo;
    public UIntPtr ProcessMemoryLimit;
    public UIntPtr JobMemoryLimit;
    public UIntPtr PeakProcessMemoryUsed;
    public UIntPtr PeakJobMemoryUsed;
}
